DOM Two Dimensional ScanDOM Two Dimensional Scanningning

using testDAQusing testDAQ

Hiroko MiyamotoHiroko MiyamotoT. NodaT. Noda

Faculty of Science

Department of Physics

Chiba University

Reminder: We did 2D scan for bare PMTs

• CE uniformity : Some tube to tube differences

• Gain uniformity: Almost universal behavior

Implementedby ROMEO

New: 2D scan for DOMs

CE uniformity / Gain uniformity:

• Present: Rely on Geant4 MC + the bare PMT calibration data to predict DOM acceptance. The complex structure of DOM has not been implemented in the MC.

• Easier and more reliable to MEASURE it directly!

2D Scanning System for DOM

Harness

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DOM 2D Scanning System

SetupLight Source:• NICHA 375nm UV-LED• 100-200 PEs / shot, fired 1.6kHz by pulser

2D scanning system• Spot size: ~1cm with the collimator• Scan 4 in ~5cm intervals from point to point• Do “testDAQ” ( ‘ready’ and ’go’) at each point.

DOM• Virgo, Rev4• Unsealed DOM, room temperature, ~1atm• TestDAQ : taking data with ~4PE threshold, 1e+07Gain

Analysis Method(preliminary)

(using the java program written by Chris W.)

• Calculate the photoelectron number with domcal Calibration (J.Braun?).

• Use the average of ~3,000 samples for each point of the DOM surface.

Results(preliminary…)

Harness Harness

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Harness Harness

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Results(preliminary…)

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Results(preliminary…)

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HarnessHarness

Forward region

Backward region

Backward region

Results(preliminary…)

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Results(preliminary…)

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Results(preliminary…)

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Results(preliminary…)

Summary(Preliminary…)

• Took a first data of DOM photon CE map (along 1 axis).

• “effective” diameter of photon detection area is approximately 25 cm, which is consistent with the PMT cathode area we had measured previously.

• Photons hitting from backside of DOM do not produce measurable signals. To map out this region, we must improve our triggering : currently internal trigger with 4 PE threshold.

Issues to be resolved

• It would be better to trigger DOM EXTERNALY for taking non-biased data – Internal trigger with 4PE threshold may cause bias in scanning backside of DOM sphere.

• Domcal charge estimation may contain some errors in the estimation of the total charge (photoelectron #) of each channels.

• Need to figure out a way to turn off and on data taking without recycling HV power.

Outlook

• 4 measurement and map the CE on the whole DOM surface to be implemented by the detector MC simulation.

• Produce the standard-EYE DOM scanned by this method.

Near future plan

• Absolute calibration of DOM by scattered light from N2 laser : We did for bare PMTs

It would be nicer if external trigger available